Mitochondrial DNA (mtDNA) isolated from two species of fruit bats, Aribeus jamaicensis and Aribeus lituratus, was used to test hypotheses concerning zoogeography, gene flow, and genetic structure of populations. Sixteen different lineages of mtDNA were isolated from Artibeus; 13 from A. jamaicensis and 3 from A. lituratus. The thirteen mtDNA lineages from A. jamaicensis (defined by mapping restriction sites) can be divided into three groups of lineages; these unique intraspecific groups are separated by a large amount of sequence divergence. This proposal is designed to test the hypothesis that rearrangements of mtDNA genes explain the considerable divergence between the groups. The alternative hypothesis is that the three groups resulted from numerous base pair substitutions and possibly an unusually fast rate, or "burst," of evolution. The hypothesis will be tested by cloning specific regions of the genomes and comparing corresponding regions of several genomes. The clones will be compared by blot hybridization, electron microscopy of heteroduplex DNA, and DNA sequencing. Although this hypothesis poses a radical departure from the commonly held belief that mtDNA gene order is conserved in mammals, it explains the presently available Artibeus data. If the proposed experiments support the hypothesis, the way in which mtDNA analysis is applied to systematic and population studies of vertebrates would be significantly altered. Additionally, the data would suggest that mtDNA rearrangements within mammals or other vertebrates might be more likely than previously thought possible. The sequencing work could shed light on whether or not certain regions of the mtDNA are "hot spots," i.e., moe likely to be involved in rearrangements. This work will be significant to geneticists, evolutionary biologists, and others using mtDNA analysis to study zoogeography and population structure in vertebrates. It is important to know if gene rearrangements occur intra- and interspecifically in mammals. This information will help investigators understand variation and conservation of mtDNA sequences, molecular evolution, and the uses and limitations of mtDNA analysis for the study of related populations, genetic structure of populations, speciation, and occurrence and affect of genetic bottlenecks.